CpG DNA has immunomodulatory effects that may eventually be useful for a wide variety of therapeutic applications, such as vaccination and immunotherapy for cancer and allergy. The overall goals of the proposed work are to understand how CpG may alter humoral immunity to polysaccharide (PS) and PS-protein conjugate antigens, and to better understand how CpG DNA may alter antigen processing and the presentation of peptide epitopes to T cells. The applicant's first specific aim is to determine the effects of CpG DNA on responses to polysaccharide (PS) and peptide epitopes of carbohydrate and glycoconjugate vaccines. The effects of CpG oligodeoxynucleotides (ODN) on immunity induced by PS immunogens and PS-protein conjugates (PS coupled to a carrier protein), as well as the carrier protein will be tested. The applicants hypothesize that CpG ODN will enhance humoral responses to carbohydrate epitopes of glycoconjugate vaccines and may alter the antibody isotypes that are elicited (e.g. to induce IgG2a responses in mice). Experiments are proposed to test whether CpG ODN can enhance antigen-specific IgM responses induced by PS antigen alone, and whether CpG-induced alterations in responses to PS immunogen are accompanied by isotype switching. Harnessing the ability of CpG ODN to enhance humoral immunity to PS antigens would allow the development of improved vaccines for encapsulated bacteria (S. pneumoniae, H. influenzae, etc.). The applicant's second specific aim is to determine the effects of CpG DNA on the processing and presentation of exogenous protein antigens by macrophages, dendritic cells and B cells in vitro, and to determine the mechanism whereby CpG DNA mediates such effects. Effects on class II MHC (MHC-II) antigen processing and presentation will be examined in a system using isolated antigen presenting cells and model antigens whose presentation can be detected by T cell hybridomas responding to specific antigenic peptides. The influence of CpG DNA on factors such as half life of surface peptide:MHC-II complexes, MHC-II synthesis and expression, and components of antigen processing machinery will be examined.